1. Field of the Invention
The present invention relates to a molding composition which is suitable for enclosing mainly electronic parts, especially semiconductor devices, and which is useful for preparing molded products having a surface amenable to laser marking.
2. Description of the Prior Art
Conventionally molded resin pieces are marked with a special thermosetting ink. However, this marking method has the problem of requiring much time and making blurred or readily removable marks.
To overcome this problem, techniques have recently been developed for marking such pieces with a laser beam. For example, the resin surface is roughened with a laser beam to make a mark and create an enhanced contrast between the mark portion and the other or background portion of the surface. The laser beam is also used for destroying coloring agents contained in compositions to afford a contrast. The coloring agents used in such compositions heretofore disclosed include ultramarine (Unexamined Japanese patent application SHO 56-144995), black organic dye (Unexamined Japanese patent application SHO 60-47065) and carbon black (Unexamined Japanese patent application SHO 60-202119).
Nevertheless, the composition incorporating an organic pigment has the drawback that the pigment must be used in a large amount and impairs the insulation and reliability of electronic parts for which the composition is used. Although black organic dyes, especially chromium-containing black azo dyes, have satisfactory marking characteristics, those for use in laser marking have nitro groups on the dye skeleton, are low in thermal stability, cannot therefore be finely pulverized, encounter difficulty in affording a uniform composition, and significantly are positive when tested for mutagenicity.